It is common in the design of internal combustion engines to provide for each cylinder an exhaust port that opens through the closed end of the respective cylinder and is controlled by a poppet exhaust valve. The port provides a passageway through which exhaust gases are conducted from the cylinder after combustion therein for disposal by the engine exhaust system.
The exhaust port and its associated poppet valve are generally made as large and as curve free as possible in order to provide a smooth and relatively restriction free path for passage of the exhaust gases out of the cylinder when the exhaust valve is opened. In actual practice, it is, of course, necessary to limit the size and location of both the exhaust valves and their respective exhaust ports in a manner that best meets all the various design requirements relating to the engine construction. Thus, it is often the case that the exhaust port will be designed with a relatively sharp angular bend connecting a throat portion near the valve seat with an exit portion extending laterally out through a side wall of the port defining cylinder or engine block.